Transient characteristics and performances of passive recirculation system for liquid rocket engine precooling

Abstract

This paper presents a numerical study on the transient cooldown process of liquid rocket engine by a passive recirculation precooling system. An unsteady mathematical model is developed by considering the interaction of heat dissipation from solid structure with the time- and location- dependent two-phase flow, and the predicted values show good agreements with experiments. The results demonstrate the roles of boiling regimes, and reveal distinct thermal and flow characteristics from single pipe cooldown and bleed precooling. The liquid rewetting front propagates along the flow direction in the vertical feed line and the turbopump related horizontal pipes, with the exception that opposite propagation appears in the upward recirculation line and causes inverted axial temperature distributions and faster cooling of exit. In terms of the time for meeting the turbopump operation requirement, large-diameter recirculation line and high liquid level in the ullage discharging condition are advantageous to the precooling of cryogenic pump, while subcooled liquid and high liquid level in liquid discharging condition prolong the cooldown process and are undesirable. The dependence of cooldown time on subcooling degree, relative liquid level and recirculation line diameter can be described by linear, cubic and exponential functions, respectively.